87 Golf 16V idles at 3000RPM!!!

[rbou]

Just got this vehicle so I have no history, it is a 87 GTI 16V, 5 speed, with about 150K miles and engine sounds solid BUT, it starts fine and runs right for about 20 or 30 seconds then the RPMs increase to 2500RPMs. The last time I started it ,it started ok but then went to 3000RPMs.I have tested the cold start valve,idle air stabilizer,thermotime switch,all seem ok and I can't find any obvious air leaks.Anyone know any easy solutions? TIA

[boschmann]

If you clamp off the idle stabilizer valve's large vacuum hose once the engine is warmed up does it affect the idle?

[rbou]

Originally Posted by boschmann

If you clamp off the idle stabilizer valve's large vacuum hose once the engine is warmed up does it affect the idle?

When I clamp off the hose where it comes off the air cleaner the idle drops by about 300 RPM. When I clamp off the hose near the idle stabilizer the idle does not change. I can reduce the idle by turning the distributor counter-clockwise but then it backfires when I open the throttle. I think the RPM is too high at this point to check the timing. I hope you can help me with this problem as the body on it is in nice shape,with only a cracked windshield, but the interior is rough.I really hate to junk it.Thanks

[boschmann]

You can't set the timing until the RPM's are down. You checked all the vacuum lines & brake booster line & fuel injector seals for leaks? Pull the air boot off the air flow meter plate & check that it doesn't hit the side or stick/bind. The accelerator cable is not too tight & easily closes against the stop? Does it look like anyone has turned the closed throttle stop, there should be a paint seal to indicate if it has been changed. Remove the idle valve & look into it, the valve should be full open. Connect the harness back & turn on the ignition, the valve should partially close if it's working. Test the coolant temp sensor (it controls the stabilizer valves postition). Resistance should be 2000-3000 Ohms cold, 200-300 Ohms at operating temp. If your car has A/C there should be two idle boost solenoids. Clamp their hoses off to see if one is activated, it wouldw idle down.

[rbou]

Thanks for the help, you're right on the money! I made most of the recommended checks, when I had the boot off to check the airflow meter plate I noticed the "high speed throttle plate"? was not fully closed. As you suggested I reinspected and found the linkage was corroded, cleaned it up, the throttle plate closed, and seems to idle correctly. Thanks again for the input.